Fix auto-reexporting the root of an NFS v4 server

When exporting the root "/" of an NFS v4 server with AUTO_REEXPORT
enabled; attempting to navigate to nested volumes would result in an
error such as "/mnt/files is not a directory".

This is because the logic that ensures the root export always has
"fsid=0" was overriding the re-export logic. The updated logic correctly
applies both conditions to the export.

Change-Id: Iaa47fc46df16281e91037405b5d1c332b779e995

Author: chris-chilvers-qodea

deployment/terraform-module-knfsd/resources/proxy-startup.sh

@@ -135,24 +135,34 @@ NEXT_FSID=1
 function add_nfs_export() {
   local FSID
 
-  if [[ $1 == / ]]; then
-    # Special handling when re-exporting root exports.
-    # For NFS v4 the FSID of the root should be set to 0.
-    FSID="fsid=0"
-  elif [[ $FSID_MODE == "static" ]]; then
+  if [[ $FSID_MODE == "static" ]]; then
     # Statically assign fsid numbers to exports without using the fsidd service.
     # This doesn't really have any advantage over FSID_MODE=local, but can be
     # useful for testing, debugging or troubleshooting.
-    FSID="fsid=${NEXT_FSID}"
-    NEXT_FSID=$((NEXT_FSID+1))
+
+    if [[ $1 == / ]]; then
+      # Special handling when re-exporting root exports.
+      # For NFS v4 the FSID of the root should be set to 0.
+      FSID="fsid=0"
+    else
+      FSID="fsid=${NEXT_FSID}"
+      NEXT_FSID=$((NEXT_FSID+1))
+    fi
   else
     # For FSID_MODE local or external use reexport=auto-fsidnum to automatically
-	# assign fsid numbers using the fsidd service.
+    # assign fsid numbers using the fsidd service.
     # When FSID_MODE is set to external this will ensure that all the knfsd
-	# instances in a cluster have the same fsid for each export.
+    # instances in a cluster have the same fsid for each export.
     # This is less useful when FSID_MODE is set to local, but it will still
     # ensure the knfsd instance uses the same fsids after a reboot.
-    FSID="reexport=auto-fsidnum"
+
+    if [[ $1 == / ]]; then
+      # Special handling when re-exporting root exports.
+      # For NFS v4 the FSID of the root should be set to 0.
+      FSID="fsid=0,reexport=auto-fsidnum"
+    else
+      FSID="reexport=auto-fsidnum"
+    fi
   fi
 
   echo "Creating NFS share export for $1..."

docs/changes/changelog.md

@@ -3,6 +3,7 @@
 * Fetch Ubuntu Kernel source from launchpad
 * Display Kernel and OS version information at end of packer build
 * Fix proxy startup script always prints "Error starting proxy"
+* Fix auto-reexporting the root of an NFS v4 server
 
 ## Fetch Ubuntu Kernel source from launchpad
 
@@ -17,6 +18,12 @@ useful when looking at past build logs.
 
 The proxy startup script would always print the error message "Error starting proxy", even after the "Reached Proxy Startup Exit. Happy caching!" message. This was due to a typo when checking the startup_complete variable.
 
+## Fix auto-reexporting the root of an NFS v4 server
+
+When exporting the root "/" of an NFS v4 server with AUTO_REEXPORT enabled; attempting to navigate to nested volumes would result in an error such as "/mnt/files is not a directory".
+
+This is because the logic that ensures the root export always has `fsid=0` was overriding the re-export logic. The updated logic correctly applies both conditions to the export.
+
 # v1.0.0-beta7
 
 * Fix error applying Terraform when nodes greater than 1